Ignition system



Oct. 27, 1959 J, v. MGNULTY ETAL 2,910,622

IGNITION SYSTEM Filed March 18, 1957 s Sheets-Sheet 1 AT Tfi- G E i 6% 4 z 1 r 6 I v 3 I W INTERNAL I I IMPEDANCE 6 SOURCE GATE INVENTORS JOHN M MC/VULTV ATTORNEY I IHIIHIHII Oct. 27, 1959 J v MCNULTY ETAL 2,910,622

IGNITION SYSTEM Filed March 18, 1957 3 Sheets-Sheet 2 Tia. 5. 3

GATE

GATE

INVENTORS JOHN 1 MC/VULTY BY DA V/D J Mam/r ATTOENEV Oct. 27, 1959 J. v. MCNULTY EIAL IGNITION SYSTEM 3 Sheets-Sheet 3 Filed March 18, 1957 INVENTORS JOHN 1/. Me A/uz r) 04 W0 J W/P/GHT ATTORNH United States Patent IGNITION SYSTEM John V. McNulty and David J. Wright, Norwich, N.Y.,

assignors to General Laboratory Associates, Inc, Norwich, N.Y., a corporation of New York Application March 18, 1957, Serial No. 646,918

9 Claims. or. 315-183) This invention relates to ignition apparatus generally, and particularly to apparatus suitable forigniting mixtures of fuel and combustion supporting materials. While the invention is described as applied to an ignition apparatus suitable for use in jet or rocket engines, it may be applied to other fuel burning engines and devices with advantage.

The problem of igniting fuel mixtures in engines of the type described presents many difliculties, due to the wide range of pressures and temperatures which maybe encountered at the locality of the igniter and also due to the wide range of variation of the mixture proportions,

i.e., the proportion of fuel to the combustion supporting material, usually air.

It has been the general practice in ignition systems for internal combustion engines to provide comparatively low energy sparks, e.g., of the orderof 0.006 joule. In jet and rocket engines, the spark must be of substantially higher energy. Sparks of l to 20 joules are common, and energies as high as 40 joules have been used in special and experimental cases. It is, in fact, desirable for the discharge between the electrodes of the igniter in such an engine to be in the form of an are as distinguished from a glow discharge. While the heavy current are results in appreciable erosion or" theigniter electrodes, only a relatively short total operating life is expected of the igniter, since it does not run continuously when the engine is running, but only during starting operations. Furthermore, such erosion. may be minimized, as described herein, by controlling the duration of each discharge.

An object of the present invention is to provide improved apparatus for igniting mixtures of combustion supporting material and fuel in jet and rocketengines and the like.

Another object is to provide improved ignition apparatus for creating an arc discharge at anigniter gap.

A further object is to provide improved apparatus for controlling the duration of an arc discharge of the type described.

A further object is to provide improved apparatus for interrupting a heavy current so as to terminate an arc discharge.

The foregoing objects and advantages are attained, in the apparatus described herein, by providing an igniter gap constructed to withstand substantial arc discharges and a source of electrical energy having a low internal impedance and an output potential when loaded by an are at that gap which is greater than the minimum or sustaining potential. A low impedance circuit connects this source to the igniter. A gate control for initiating and terminating arc discharges at the gap isconnected in series between the source and the low impedance gap circuit. The gate control may include trigger means for initiating the arc. Means are provided for controlling the time. or duration of arc discharges at the gap. This time control includes a timing device for establishing an interval of predetermined duration, at the termination ice 2,. of which the arc discharge is extinguished. Two modifications of such time controls are disclosed, one in which the predetermined interval begins with the energization of the trigger, and another in" which the interval begins with the initiation of the arc.

In the preferred form of the apparatus described herein, the arc current is interrupted by a magnetic amplifier, so that no separation of contacts is required to interrupt the current.

The trigger means disclosed herein includes a high frequency transformer having a secondary winding connected in the igniter circuit, for the purpose of supplying the high frequency, high potential energy required to break down the gap at the igniter. This secondary winding is constructed and arranged to provide a low reactance upon initiation of the discharge, i.e. a low irnpedance path to thearc current. In one modification a saturable choke coiliis connected in parallel with the trigger secondary winding, andiscaused to saturate when the arc discharge current flows, thereby decreasing the impedance of thecircuit to that current;

Other objects and advantages of the invention will become apparent from a consideration of the following description, taken. together with. the accompaying drawings and the appended claims.

In the drawings: a

Figure 1 is an electrical wiring'diagram showing a simplified arc discharge ignition system embodying cer tain features of the invention;

Figs. 2, 3, 4 and. 5 are electrical wiring. diagramsshowing alternative modifications of the invention;

Fig. 6 is a fragmentary wiring diagram showingaone type of gatestructure and gate operating mechanism;

Fig. 7 is a fragmentary wiring diagram showing a different type of gate and gate operatingmechanism;

Figs. 8. and 9 are electricalwiringdiagrams showing further modifications of the invention; and

Fig. 10 is a graphical illustration relating to part of the operating cycle of the circuit of Fig. 9..

Fig. 1

There is. shown in this figure. an. igniter generally indi- When an arc discharge takes place-atthe igniterfil, a

heavy currentflows from. the sourcel8t and through the transformer windings 6 and 4. Thesource 8. and the transformer windings 6-and 4 musthaveinternal. impedances low enough with relation to. the. source-potential to carry this heavy current. The transformer 5 is-a step-up transformer, and its secondary terminal potentialat no load must be. high enough to exceed. the break down potentialof the igniter 1: If the. sourceti has a sufficiently high: potential, the transformer may be omitted.

The gate 7 may be any'device shiftableibetween a low impedance or open condition'inlwhich it carries the arc current and a high impedance or.cl'osed condition in which it interrupts the arc current or reduces it below its minimum arc sustaining value. It may be a circuit breaker or"sWitch-, onitmaybe one of the more-complexdevices described in detailbelow.

While. the gate; may in: some instances be manually controlled, it is greatly, preferred, especially in ignition breaks down,'and an arc discharge begins which is This figure illustrates a circuit similar in many respects to that of Fig. 1, but differing in that it includes a trigger arrangement for breaking down the gap at the igniter. Consequently, this system can use a lower supply voltage, for a given gap spacing, than the system of Fig. 1. Those elements which correspond to their counterparts in Fig. 1 have been given the same reference numerals. The igniter 1 of Fig. 2 is connectedin a series circuit including the transformer secondary winding 4, and another transformer secondary winding 9. The transformer windings 4 and 6 are of low impedance, and are so related to the output current and potential characteristics of the source 8 so that the potential supplied through transformer 9 to the igniter 1 is capable of maintaining an are between the electrodes 2 and 3 after a discharge across the gap has been initiated, although it need not necessarily be capable of breaking .down the gap to initiate a spark.

A trigger for initiating a discharge between electrodes 2 and 3 is provided and includes a trigger transformer 10 having a primary winding 11 and a secondary winding 12. Alternatively, winding 12 might be placed on the core of transformer 5. Primary winding 11 is, connected in parallel with primary winding 6. A capacitor 13 is connected across the terminals of secondary winding 12. A discharge gap 14 is connected in series between one terminal of secondary winding 12 and the primary Winding 15 of a high frequency trigger transformer 16, which also includes the secondary winding 4, previously mentioned. The other end of secondary winding 15 is connected to the other end of secondary winding 12. Transformer 16 should preferably have a core of magnetically saturable material.

Operation of Fig. 2

When the gate 7 is closed, no current flows through any of the circuits described. When the gate 7 is first opened, no appreciable current flows through the transformer since its secondary winding is connected to an open circuit at the igniter 1. However, current flows through the trigger transformer primary 11, resulting in the development of potential across the secondary 12 and the charging of capacitor 13 until its potential is sufficient to break down the sealed gap 14, whereupon a high frequency discharge takes place through the gap 14 and is transmitted through transformer 16 to the loop circuit through the igniter 1. The transformers and 16 are so designed that the potential thereby induced in secondary winding 9 is sufficient to break down the igniter gap, thereby initiating the spark discharge at the gap.

This spark discharge decreases the impedance of the gap substantially, so that a heavy current flows through transformer 5 and thence through secondary winding 9 and through the gap, maintaining a heavy arc discharge at the gap. This discharge continues until the gate opens. The heavy current saturates the core of transformer 16, thereby reducing the impedance of winding 9, and further increasing the current flow.

Fig. 3

Those elements in this figure which correspond both in structure and in function to their counterparts in Figs. 1 and 2 have been given the same reference numerals, and will not be further described. This circuit differs from that of Fig. 2 principally by the elimination of the transformer 5 and the replacement of that trans- Fig. 4

The circuit illustrated in this figure differs from that of Fig. 2 in that the trigger is considerably simplified, consisting only of a single step-up transformer 18 having a primary winding 19 and a secondary winding 20. As in the case of Fig. 3, those elements in Fig. 4 which are the same in structure and function as their counterparts in Figs. 1 and 2 have been given the same reference numerals. The trigger operates at the supply frequency. The secondary winding 20 has a much higher impedance than the secondary Winding 9 of Fig. 2, since a larger number of turns is required to obtain the necessary stepup in potential to break down the gap at the igniter 1. The step-up in voltage must be substantially higher at transformer 18 than at transformer 5. In order that this high impedance may not adversely affect the continuous arc discharge after the gap impedance has been broken down, there is connected across the terminals of the secondary winding 20 a saturable core reactor 21.

When the only current flowing through the gap of the igniter 1 is the trigger current from the secondary winding 20, then the reactor 21 is unsaturated, and it presents a high impedance to that current, so that most of the current is forced through the igniter gap. After the igniter gap breaks down, a heavy current from the transformer Winding 4 flows through the coil of the saturable reactor 21, saturating the core of that reactor and reducing its impedance to a very low value, thereby allowing the heavy arc sustaining current to by-pass the winding 20.

Fig. 5

of transformer 16, and thence through a spark gap 26 and a capacitor 27 to the opposite terminal of winding 24. The main discharge circuit extends from winding 24 through an obvious loop including secondary winding 9 and the gap of igniter 1. r The gate 7 is illustrated in Fig. 5 as comprising a magnetic amplifier 28, having a saturable core, two output windings 29 and 30 connected in series and an output or saturating Winding 31. The saturating winding 31 is connected in series with a source of unidirectional electrical energy, shown as a battery 32, and a switch 33.

Operation of Fig. 5

When it is desired to get an are at the igniter 1, the switch 33 is closed, resulting in a flow of current through the winding 31.

The core of reactor 28 is thereby saturated and the impedance of the coils 29 and 30 is low. The operation of the circuit is then very similar to that described in connection with Fig. 2, resulting in a substantial are at the igniter.

If the switch 33 is thereafter opened, no current flows through the winding 31, the core of reactor 28 is un saturated and the impedance of the coils 29 and 30 is relatively high. The current flow through primary winding 23 is reduced, and the energy available at the igniter 1 is reduced to the point where the arc is not sustained.

gar ens Fig. 6

This figure illustrates a gate control mechanism con structed in accordance with a feature of the invention, including a time control responsive to an are at the igniter 1. A gate is generally indicated'by the reference numeral 35 and may be used to replace the gate 7 of Figs. 1 to 4 or alternatively to replace the switch 33 in the gate 7 in 5. Connected inseries with the gap of igniter 1 is a capacitor 36 in parallel with a relay winding 37 having a contact 38. The capacitor 36 by-passes the high frequency trigger discharge so that it does not substantially affect the relay winding 37. However, the heavy are current flows through the relay winding and causes it to pick up its armature, thereby closing the relay contact 38 and establishing a circuit from one terminalof the source 8 through the winding 39 of a time delay relay generally indicated by the reference numeral 40. The time delay relay 40 may include any conventional device illustrated diagrammatically by the rectangle 41, for delaying movement of the relay armature in response. to changes in energization of the winding 31. For example, the device 41 may have a characteristic such that the relay 40 will not pick up its armature until several cycles ofalternating current have passed through the winding. The relay 40 controls a switch 42 which may replace either the gate 7 of Figs. 1 to 4 or the switch 33 of Fig. 5.

Whenthe gate mechanism of Fig. 6 is used, the re suit is that an are at the igniter 1, once established, continues for a time determined by the characteristic of the relay 4! and is then discontinued by the opening of the gate 35. When gate 35 opens, relay winding 37 is deenergized, opening contact 38 and in turn deenergizing relay 40. After a time determined by the characteristics of the delay device 41, contact 42 again closes. The are is then reestablished and continues intermittently in a time cycle determined by the device 41.

Fig. 7

This figure illustrates a somewhat different form of gate operating mechanism, and includes a gate 43 including a cam 44 operating a switch 45. The cam 44 is driven by an electric motor 46 which is energized by connection across the source 8 through a circuit which includes the switch 45.

The arrangement is such that ignition is started by closing the push-button switch 47, connected in parallel with switch 45, whereupon the motor starts and closes the switch 45, through which the motor continues to be energized after the switch 47 is opened. The spark is then initiated and is followed by an arc discharge, as described above, which are discharge continues until the switch 45 is again opened after a predetermined time by actuation of cam 44. Although the cam 44 is shown as having only a single switch-opening lobe, it should be readily apparent that it may be constructed with several lobes.

Although the various switches in the gate mechanism illustrated have been shown diagrammatically, it will be readily understood that the actual switch mechanism used in any such apparatus must be capable of interrupting a current of substantial magnitude. The gate 43 may be substituted for the gate 7 in any of the previous figures.

Fig. 8

This figure illustrates another modification of the invention, including particularly a novel form of time delay mechanism for operating the gate.

The gate includes a relay 48 having two normally open switch contacts 49 connected electrically in parallel to provide high current carrying capacity. The contacts 49 are connected in a simple loop circuit with the alternating current source 8 and a primary winding 50 of a transformer 51 having a secondary winding 52. In'the high frequency trigger circuit, a condenser 53 is con- 6 nected across the terminals of secondary winding 52. A condenser 54 is connected across the primary winding. 15 and the gap 26 in series. A resistor 55 is connected between gap 26 and ground.

The relay winding 48 is energized through a circuit which may be traced from the upper terminal of source 8 through a wire 57, the winding of relay 48, a wire 58, normally closed contact 59 of a relay 69 and a diode 61 to the opposite terminal of the source 8. Relay is energized through a circuit which may be traced from the upper terminal of source 8 through wire 57, winding 60, a resistor 63, contact 59 and diode '61 to the lower terminal of the source 8. A condenser 64 is connected between the Wire 57 and the opposite terminal of the relay winding 60. Another condenser is connected between wire 57 and the opposite terminal of relay winding 48. Three condensers 66, 67 and 68 are connected between the wire 58 and a selector switch 69, which is in turn connected to wire 57.

All the parts ofthe system of Fig. 8, except the source 8 and the igniter 1, may conveniently be mounted'in one unit, indicated by the dotted line frame 34. The ungrounded side of the igniter 1 should be connected to the unit 34by a shielded cable 1a.

Operation of Fig. 8

A manual on-off switch may be provided (not shown), by which the system may be turned on when desired. When the system is de-energized, the relay contacts are in the positions shown in the drawing, with the contact 59 closed and the contacts 49 open. When the system is initially energized, a circuit is completed for relay winding 48, through the contact 59 and diode 61. The circuit through relay winding 60 is also completed through resistor 63 and contact 59. The winding 48 has a higher voltage drop across it, because the voltage drop across resistance 63 cuts down the voltage available at the terminals of the winding 60. Condenser 65 and condenser 68 (or 66 or 67, as selected by the position of switch 69) are connected in parallel across the relay winding 48. When the circuit is initially energized, these condensers provide an effective shunt across the relay Winding 48 until such time as they become charged substantially to the potential of the source 8. However, since there is little or no resistance in series with these condensers, they charge rapidly. The condenser 64, because of the resistance 63 in series with it, charges more slowly, so that the winding 60 is not effectively energized until some later time, Consequently, a condition is set up in which the relay 48 is energized quickly and the relay 60 is energized after a somewhat longer time.

When the relay 48 is energized, the contacts 49 close, sending current through the primary winding 50. A current flow is thereby induced in the secondary winding 52, charging the condenser 53 and building up a charge on the condenser 54 until the gap 26 breaks down, Whereupon a high frequency discharge takes place through the primary winding 15, inducing a high frequency potential of substantial magnitude in the secondary winding 9, the latter potential being sufiicient to break. down the gap at the igniter 1. When the gap at igniter 1 breaks down a heavy current flows from winding 52 through resistor 56- and the igniter 1, resulting in an arc discharge at the igniter. This discharge continues until the condenser 64 becomes charged, at which time the relay winding 66 is energized and opens the contact 59, thereby opening the energizing circuit for relay winding 48. The contacts 49 thereupon open, terminating the flow of current through winding 50 and thereby terminating the arc discharge.

It should be. noted that the timing of an individual arc discharge in the. circuit of Fig. 8 is determined by the characteristics of the energizing circuits for the relays 48 and 60, and is entirely independent of the flow of current through the are atthe igniter.

7 Figs. 9 and 10 This circuit illustrates another embodiment of the invention, in which the arc discharge through the igniter is terminated a predetermined'time after the discharge begins. Furthermore, the arc is terminated without the use of current interrupting contacts. As in the previous figures, those elements in Fig. 9 which correspond in structure and in function to elements described in the preceding figures have been given the same reference numerals and will not be further described.

In Fig. 9, the circuit between the source 8 and the primary winding 50 extends through a magnetic amplifier generally indicated at 78. The amplifier 70 includes two separate magnetic cores 71 and 72, of a magnetic material having a rectangular hysteresis loop. The cores 71 and 72 must be closed loops instead of being openended, as shown diagrammatically in the drawing. The core 71 is provided with an output winding 73, a crossconnected feedback winding 74, and a control winding 75. The core 72 is similarly provided with an output Winding 76, a cross-connected feedback winding 77, and a control winding 78.

The circuit connecting the source 8 and the transformer primary winding 50 has two branches, one including in series a diode 79, winding 74 on core 71, and winding 76 on core 72. The other branch includes in series a diode 80, winding 77 on core 72, and winding 73 on core 71. The two diodes 70 and 80 are oppositely poled, as shown, and each diode provides half wave rectification of the alternating current from the source 8. The alternate half-wave currents flowing in the windings 73 and 76 tend to saturate the cores 71 and 72, respectively, in one direction, this saturating tendency being aided by the other half-wave currents in the opposed polarity windings 74 and 77. When the control windings 75 and 78 are not energized, the cores 71 and 72 are saturated, so that the windings 73, 74, 76 and 77 have low impedance.

The secondary winding 52 is connected to two igniters 81a and 8112 through a circuit somewhat more elaborate than the previous modifications.

The main discharge circuit between secondary winding 52 and the igniters 81a and 81b, may be traced from the upper terminal of winding 52, as it appears in the drawing, through a wire 82, secondary winding 83 of a high frequency saturable core transformer 84, igniter 81a to ground, from ground through igniter 8117, secondary winding 85 of a high frequency saturable core transformer 85, a resistor 87, and a wire 88 to the lower terminal of secondary winding 52.

For the purpose of supplying high frequency current to the transformers 84 and 85, there is connected across the terminals of winding 52, a high frequency generating circuit, including a condenser 89 connected in series with a resistor 90, and another condenser 91 connected in series with a resistor 92. A discharge gap 93 is connected between wire 82 and a junction 94. The junction 94 is connected through primary winding 95 of transformer 84 to the common terminal of condenser 89 and resistor 90. The junction 94 is connected through primary winding 96 of transformer 86 to the common terminal of condenser 91 and resistor 92. The end of secondary winding 83 farthest from the igniter 81 is connected to ground through a condenser 83a, which provides a low impedance by-pass for high frequency currents. A similar high frequency by-pass condenser 85a is provided for winding 85.

Connected across the resistor 87 is a rectifier bridge circuit generally indicated by the numeral 97, its four branches respectively including a diode 98, a diode 99, a resistor 180, and a resistor 101. The junction between the diodes 98 and 99 serves as one input terminal for the bridge, and the junction between resistors 100 and 101 serves as the other input terminal. The input terminals are connected across resistor 87. The common junction of resistor 100 and diode 98 serves as one output terminal 8 and the common junction between resistor 101 and diode 99 serves as the other output terminal. A condenser 102 is mounted. across the output terminals. The output of the rectifier bridge is fed through a resistor 103 to the control windings and 78 of the magnetic amplifier 70. Condenser 102 and resistor 103 cooperate to filter the output of the bridge and to remove most of the alternating Operation of Fig. 9

The magnetic amplifier 70 has a feedback characteristic which is greater than 100%. When the windings 73, 74, 76 and 77 are energized, and the control windings 75 and 78 are de-energized, then the magnetic cores 71 and 72 are substantially saturated in one direction, and the impedance of the amplifier to currents flowing between the source 8 and the primary winding 50 is very low. When a properly poled direct current flows in the windings 75 and 78, it bucks the saturating magnetomotive force in both of the cores, thereby greatly increasing the impedance of the magnetic amplifier to the main current flow and reducing that flow substantially.

When the circuit is first energized, the impedance of the magnetic amplifier is high, but reduces rapidly to a minimum value upon the saturation of the cores 71 and 72. At this time, a substantial current flows through primary winding 50 inducing a potential in the secondary winding 52. This potential is not sufficiently great to break down the gaps at the igniters 81a and 81b. However, it starts building up a charge on the condensers 89 and 91. When this charge becomes sufiicient to break down the gap 93, a high frequency current is produced through the primary windings 95 and 96, which induces current through the secondary windings 83 and and produces there a potential high enough to break down the gaps at the igniters 81a and 81b. This high frequency current is of relatively small value, but it is immediately followed by a large arc discharge current flowing directly from the secondary winding 52, through resistor 87 and the secondary windings 83 and 85; This are discharge produces a high energy are at the igniters 81a and 8112, thereby igniting any fuel which may be present there. The heavy arc discharge current produces a substantial voltage drop across resistor 87, which is rectified by the bridge 97 and fed through the resistor 103 to the control windings 75 and 78 of the magnetic amplifier, with a time delay due to the filter resistor 103 and condenser 102.

The eifect of the current in the windings 75 and 78 .on the potential across the primary winding 50 is illustrated graphically in Fig. 10. The abscissae in that figure represent the current Ic flowing through the control windings 75 and 78, and the ordinates represent the primary voltage Vp.

Initially, the system operates at point A, with no control current and a high primary voltage. The control current increases toward point B, at which point its value is large enough to buck down the saturation of the cores in the amplifier 70, resulting in a decrease in the current flowing through the main windings 73, '76 and hence a decrease in the potential across the winding 50. This decrease in the current fiow through the windings-of the magnetic amplifier produces a further self-excitation or internal feedback effect, which further reduces the saturation of the cores and thereby further increases the impedance of the magnetic amplifier. This effect continues cumulatively along the curve BC in Fig. 10, until at C the impedance of windings 73, 74, 76 and 77 becomes high enough so that the primary voltage is almost zero and the current flow through the secondary winding 52 is no longer great enough to sustain the arc discharge at the igniters 81a and 81b. The discharge then terminates, thereby interrupting the current flow through the resistor 87. The current flow through windings 75, 78 decreases slowly, along the curve CD in Fig. 10. Until the point D is reached, there is no substantial increase in the primary voltage. When point D is reached, the control winding current terminates, the saturation of the cores 71 and 72 again builds up rapidly and the impedance of the windings 73, 7 76 and 77 again drops to a low value, resulting in the sudden increase in the primary voltage, back to point A in Fig. 10, and the initiation of another discharge at the igniters 81a and 81b.

It may therefore be seen that the system illustrated produces an intermittent arc discharge at the igniters 81a and 81b, without the interposition of any contacts in the circuit which have to be opened or closed. The values of the impedance elements determine the duration of each discharge and the time separation between the successive discharges. More specifically, these impedances determine (1) the delay due to the hysteresis effect illustrated diagrammatically in Fig. 10, and (2) the time delay due to resistor 103 and condenser 102. The intermittent character of the discharge greatly improves the performance of the contacts at the igniter gap, and lengthens their life, as compared to the performance and life obtained with a continuous discharge.

While we have shown and described certain preferred embodiments of ourinvention, other modifications thereof will readily occur to those skilled in the art and we, therefore, intend our invention to be defined only by the appended claims.

We claim:

1. Ignition apparatus, comprising means defining an ignition gap, a source of electrical energy having an output potential when loaded by an arc across the gap greater than the minimum continuous arc-sustaining potential of the gap and having an open circuit output potential less than the breakdown potential of the gap, trigger means for supplying a high potential trigger impulse to said gap to initiate an electrical discharge thereacross, a low impedance circuit connecting said source and said gap in series and cooperating with said source to sustain an arc across said gap after initiation of said discharge by said trigger means, a gate connected in said circuit and operable to interrupt the flow of current therethrough, timer means operatively connected to the inter rupter means and cooperating therewith to extinguish the arc upon expiration of a predetermined interval, and means to initiate the timing of the interval by the timer means.

2. Ignition apparatus as defined in claim 1 in which said means to initiate timing of said interval is eifective to initiate said timing of said interval concurrently with operation of the trigger means.

3. Ignition apparatus as defined in claim 1, in which said timer means comprises an electric motor supplied with energy from said source, a cam driven cyclically by said motor, and switch means actuated by said cam and controlling said trigger means and said gate.

4. Ignition apparatus as defined in claim 1, in which said timer means comprises a time delay relay, and means responsive to the flow of the arc current in said low impedance circuit for initiating operation of the time delay relay.

5. Ignition apparatus as defined in claim 1, in which said gate comprises a relay having normally open contacts connected in said circuit, an energizing circuit for said relay, said relay being effective when said energizing 10 circuit is completed to close said contacts and thereby to initiate an arc discharge at said gap, and time-controlled means for periodically closing and opening said energizing circuit.

6. Ignition apparatus as defined in claim 1, comprising an electric circuit including said gap, a transformer having a secondary winding connected in said gap circuit in series with said gap, means including said transformer for inducing in said secondary winding a potential greater than the breakdown potential of the gap and effective to initiate a low current discharge through said gap, means for supplying to said circuit electrical energy at a relatively higher current and potential sufficient to maintain an arc discharge at said gap, said last-mentioned potential being less than the breakdown potential of the gap, and a saturable core reactor connected in parallel with said secondary Winding and ellective to present a high impedance to said high potential, the core of said reactor being saturated by said hi h arc-discharge current, so that the reactor provides a low impedance shunt past said secondary winding for said high current.

7. Current interruptingmeans for an electric circuit comprising a source of alternating electrical energy; a magnetic amplifier including a saturable core, a load winding and a control winding on said core; an output, means operatively connecting said source and said load winding to said output, feedback means including rectifier means to derive from said output a unidirectional current, and means to conduct said unidirectional current through said control winding with a polarity eifective to reduce the saturation of said core, and thereby to increase the effective impedance of said load winding to interrupt substantially the currentfiow through said output.

8. Current interrupting means as defined in claim 7, including time delay means in said feedback means to delay. transmission of said unidirectional current to said feedback winding.

9. Ignition apparatus, comprising means defining an ignition gap, a source of electrical energy, a low impedance circuit connecting said source and said gap in series and cooperating with said source to sustain an are discharge across said gap, a gate connected in said circuit and operable to reduce the flow of current therethrough below the minimum arc-sustaining value, time-controlled means operatively connected to said gate and cooperating therewith to extinguish the arc upon expiration of a predetermined time interval, and means to initiate the timing of said interval by said time-controlled means, said gate comprising a magnetic amplifier having an output winding connected in said circuit and control winding, and feedback means connected in said circuit for energizing said control winding, said feedback means including said time-controlled means, said feedback and said time-controlled means cooperating to apply to said control winding a potential efiective to cut oif substantially the arcsustaining current after a predetermined interval following each initiation of said current, and to cut off said potential at a predetermined time after each cut-off of the arc-sustaining current, so that the arc-sustaining current is again initiated.

References Cited in the file of this patent UNITED STATES PATENTS 1,225,536 Varley May 8, 1917 2,227,714 Holthouse et al. Jan. 7, 1941 2,470,413 Ramsay May 17, 1941 2,495,155 Ankenman Jan. 17, 1950 2,551,101 Debetiham et a1. May 1, 1951 2,632,133 McNulty Mar. 17, 1953 2,727,188 Rively Dec. 13, 1955 2,784,349 Anderson Mar. 5, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,910,622 October 21, 1959 John V McNulty et a1 a in the printed specification ied that error appears on and that the said Letters It is hereby certif of the above numbered patent requiring correcti Patent should read as corrected below.

6, for output"' a input Column 4 line 5 s 4th day of April 1961 Signed and sealed thi (SEAL) Attesh ERNEST W. SWIDER ARTHUR W. CROCKER hg 59cm Acting Commissioner of Patents 

